1. Field of the Invention
The present invention relates generally to footwear, and more particularly, to footwear having piezoelectric-based toe-heaters for frostbite protection.
2. Prior Art
During many outdoor activities in the winter time or in a cold environment, such as during mountain climbing, hiking, skiing, or performing varieties of tasks such as repairs, clean-up operations and the like, the feet inside shoes and boots can get very cold, and can lead to frostbite, particularly at the extremities, i.e., the toes. At the very least, such conditions can be very uncomfortable for the person exposed to the cold environment. A solution has been to provide certain means to warm the feet, particularly the toes. Appropriate amount of insulation has also been provided to minimize the amount of the heat that is needed to keep the entire feet more uniformly warm.
The provision of proper and highly effective insulation to keep heat inside and moisture outside the shoe and minimize heat loss is very well known in the art and is being widely practiced.
The provision of heating elements to generate heat inside the shoes has also been disclosed, for example, in the following patents.
U.S. Pat. No. 4,674,199 discloses a shoe with an internal warming mechanism which comprises an electrical resistance coil in the sole or upper coverings of the shoe, and with an electrical generation mechanism in the heel of the shoe which is driven by the up-and-down movements of the heel. The electrical generator includes an armature mounted for rotational movement in a magnetic field and mechanically connected to a vertical post which is dependent on the undersurface of the heel portion of the inner sole of the shoe. The post is connected through a vertical spiral groove to a sleeve which is coupled with an escapement to a flywheel that is unidirectionally driven by the sleeve. The flywheel is coupled through a gear train to the armature of the electrical generator.
U.S. Pat. No. 5,722,185 is directed to a heated shoe having a heel, a sole provided with a heating device and an outside face for making contact with the ground, and at least one energy-providing battery located in the heel and connected to the heating device. In this patent, the heating device comprises a heating film or cloth extending over at least a portion of the sole parallel to its outside face. The sole also includes a structure of closed cells extending between the heating film or cloth and the outside face of the sole.
U.S. Pat. No. 6,041,518 discloses a battery powered climate-controlled shoe which controls the climate surrounding a user's foot in the shoe during a wide range of weather conditions. The shoe contains a plurality of switches, one of which is an interlock for inhibiting operating of the system until a pressure sensitive switch is activated by the insertion of a foot into the shoe. The shoe also contains a fan and a metallic heating plate. The fan aids in the circulation of air within the shoe, and the heating plate provides warm air for circulation within the shoe during cold weather.
U.S. Pat. No. 6,041,518 discloses a frictional heat generator and a forced air circulation system for shoes and boots such as ski boots. The shoe has an inner sole which is formed of a pair of sole plates which are mounted for relative sliding movement in the shoe. The upper sole plate is pivotally attached at its toe end to an outer sole of the shoe. The lower sole plate of this pair is pivotally mounted with a crank arm which is located at its heel end. Twisted torsion cables are provided to bias the sole plates upwardly against the applied weight of the wearer. A compartment is formed in the shoe between the pair of sole plates and outer sole and is enclosed with a diaphragm to function as a bellows-type air pump to circulate air through the shoe.
The inclusion of electrical energy generators in the heels that rely on the pressure exerted by the body during walking and the like makes the user spend a lot of energy during normal walking since the heel has to deform, bringing the body downward, i.e., the entire body weight has to move down a certain distance to provide mechanical energy equal to the weight of the person times the distance that the body has displaced down. This is equivalent to the person moving up steps of equal amount or walking on sand and would be very tiring to the user. Such electrical energy generation devices are also very inefficient, thereby providing a very small portion of the energy spent by the wearer to useful electrical energy for heating the feet, thereby making them impractical. In addition, such devices developed to date do not provide enough energy to warm the feet and toes enough to avoid frostbite and other maladies, particularly in very cold environments.
The second option in the prior art uses batteries to power heating elements. Batteries of various types, however, provide a very limited amount of electrical energy. Batteries, particularly rechargeable batteries, are adequate for applications in which the user is in the cold environment a relatively short periods of times. However, for applications such as hiking, mountain climbing or even for those working outdoors for several hours at a time, batteries do not provide and adequate amount of electrical energy.
A need therefore exists for methods and devices to provide the means to warm feet inside boots worn in very cold areas subjecting the feet, particularly the toes, to frostbite and other related complications or merely to provide a more comfortable situation for those exposed to cold environments for prolonged periods. Such devices should be capable of providing significant amounts of heat to the interior of shoes that are required to keep the feet, particularly the toes, warm enough to avoid various maladies or uncomfortableness. Such devices can be used in almost any footwear, for example, construction boots, hiking boots, climbing boots, arctic shoes, ski boots, and the like.